1. Field of the Invention
The present invention relates to a brushless motor.
2. Background of the Invention
Conventionally, studies for increasing detent torque have been done to exactly control a stop position when a motor is not excited. Such a brushless motor being capable of increasing the detent torque is disclosed in, for example, JP 2007-143289(A).
In accordance with the brushless motor as described in JP 2007-143289(A), a pole tooth is formed in a stator yoke, and three types of pole teeth having different areas by varying height and/or width thereof are provided. The detent torque can be increased by shifting or displacing the three types of pole teeth in combination at a predetermined angle.
However, in the afore-mentioned conventional brushless motor configuration, the stator yoke has a direct effect on rotary drive of the motor, and also has a great effect on other properties of the motor. For the above reasons, when the pole tooth is formed in the stator yoke in order to increase the detent torque, rotation torque of the motor is greatly decreased. As a result, even if the detent torque is increased, the original properties of the motor is compromised.